I installed a set of Rox risers and they make a great improvement but I can not get them to stay tight in the stock risers. I have them as tight as I can get them and with a little effort they slide lowering my handlebars. Was on a long ride today and at my hands my bars lowered almost 2 inches by the end of my ride. Checked to see if maybe the bolts came loose but they were still tight. I bought the 2" risers for 1 1/8" bars model 1R-P2PPK. Any suggestions?